1. Field of the Invention
The present invention relates to a safety apparatus for use in a high pressure liquid jet system used to clean or cut a metallic structure and more particularly to an inductive proximity switch which ensures nonoperation of the liquid jet system unless an output nozzle of the system is in the physical proximity of the metallic structure to be cut or cleaned.
2. Description of the Related Art
The use of a liquid, such as water, under high pressure to cut or clean metal has widespread industrial applications. Such as the case in hydroblasting in which water is exerted at a force of 6,000-20,000 p.s.i. in order to clean most metallic industrial equipment, such as heat exchangers. Because of the need for portability, the hydroblasting equipment normally includes a handheld hydroblasting gun coupled to a high pressure water source. The hydroblasting gun typically has at least one trigger lever which a human operator depresses in order to eject high pressure water from a nozzle of the gun.
A primary goal for the designers of hydroblasting equipment is to reduce the chance of harm occurring due to human operator error. Because the exiting water exerts a force of 6,000-20,000 p.s.i., the output of the hydroblasting gun can inflict severe injuries if the exiting water comes in contact with a human. The danger can be more readily appreciated given that at a force of 40,000 p.s.i., a jet of water can cut through metal. Thus, safety mechanisms have been developed to reduce the possibility of someone inadvertently turning on the hydroblasting gun.
A typical hydroblasting gun consists of a trigger lever provided to turn on and off a shutoff valve or dump valve which is coupled to the high pressure water source, thereby preventing a high pressure jet of water from accidentally exiting the nozzle. Several hydroblasting guns have been developed with safety mechanisms to ensure that this valve is not turned on by the inadvertent depression of the trigger lever when the hydroblasting gun is not being used to clean. Such a safety mechanism is disclosed in U.S. Pat. No. 4,216,911 entitled "High-Pressure Liquid-Jet Gun," Aug. 12, 1980. A high pressure hydroblasting gun is disclosed in which, in addition to the normal trigger lever located on the handle of the gun, a safety lever is located on the barrel of the gun, thereby requiring the operator to engage the safety lever on the barrel with one hand and the trigger lever with the other hand. This reduces the possibility of the operator inadvertently turning on the gun because both hands must be properly holding the gun in the normal cleaning position in order to turn on the gun. Another such dual trigger mechanism is disclosed in U.S. Pat. No. 4,784,330 entitled "High-pressure Spraying Gun," Nov. 15, 1988. A high pressure spraying gun is disclosed which has two handles with trigger levers on each handle which necessarily requires both hands to grip the gun in order to turn on the gun. Yet another type of safety device to be employed in a hydroblasting gun system is disclosed in U.S. Pat. No. 4,814,632 entitled "Safety Device," Mar. 21, 1989, and U.S. Pat. No. 4,914,721 entitled "Safety Device," Apr. 3, 1990. In these disclosures, a sensor is employed which senses if the operator has properly gripped the hydroblasting device, thereby reducing the risk of accidentally turning on the gun.
Although the prior art discloses systems for reducing the possibility of someone inadvertently turning on the hydroblasting gun, it still does not ensure that the hydroblasting gun will only be turned on when the gun is pointed at the metal structure to be cleaned. Because of the high recoil and weight of these guns, the chance of human operator error increases with the time of operation. Thus, a safety system is desired which inhibits operation of the hydroblasting gun unless the hydroblasting gun is directed toward the metal structure, thereby ensuring safety to the operator and all other humans who may be present. Furthermore, such a safety system could also be employed in a hydrocutting system to ensure the hydrocutter only turns on when the metal to be cut comes within the physical proximity of a nozzle of the hydrocutter.